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Science Terms Definitions - I

ICRP - International Commission on Radiological Protection.

In Vitro - Outside the living organism. Literally, in glass.

In Vivo - Within the living organism.

Incidence - The number of new cases of a disease in a population over a period of time.

Indicator Organisms - A species, whose presence or absence may be characteristic of environmental conditions in a particular area of habitat; however, species composition and relative abundance of individual components of the population or community are usually considered to be a more reliable index of water quality.

Individual Risk - The risk to an individual rather than to a population.

Induced Radioactivity - Radioactivity produced in any material as a result of nuclear reactions, especially by absorption of neutrons.

Infiltration - The penetration of water through the ground surface into sub-surface soil or the penetration of water from the soil into sewer or other pipes through defective joints, connections, or manhole walls. T he technique of applying large volumes of waste water to land to penetrate the surface and percolate through the underlying soil.

Infiltration Gallery - A subsurface groundwater collection system, typically shallow in depth, constructed with open-jointed or perforated pipes that discharge collected water into a water-tight chamber from which the water is pumped to treatment facilities and into the distribution system. Usually located close to streams or ponds.

Infiltration Rate - The quantity of water than can enter the soil in a specified time interval.

Influent - Water, wastewater, or other liquid flowing into a reservoir, basin, or treatment plant.

Injection Well - A well into which fluids are injected for purposes such as waste disposal, improving the recovery of crude oil, or solution mining.

Injection Zone - A geological formation receiving fluids through a well.

Internal Radiation Dose - The dose to organs of the body from radioactive materials inside the body. It may consist of any combination of alpha, beta, and gamma radiation.

Inversion - An atmospheric condition caused by a layer of warm air preventing the rise of relatively cool air trapped beneath it. This holds down pollutants that might otherwise be dispersed, and can cause an air pollution episode.


(1) An atom that has too many or too few electrons, causing it to have an electrical charge, and therefore, be chemically active.

(2) An electron that is not associated (in orbit) with a nucleus.

Ionization - The process of adding one or more electrons to, or removing one or more electrons from, atoms or molecules, thereby creating ions. High temperatures, electrical discharges, or nuclear radiations can cause ionization.

Ionize - To split off one or more electrons from an atom, thus leaving it with a positive electric charge. The electrons usually attach to other atoms or molecules giving them a negative charge.

Ionizing Radiation - Any radiation capable of displacing electrons from atoms or molecules, thereby producing ions. Some examples are alpha, beta, gamma, x-rays, neutrons, and ultraviolet light. High doses of ionizing radiation may produce severe skin or tissue damage.

Irradiation - Exposure to radiation.

Isotope - Atoms of the same element that have the same number of protons (and hence the same chemical properties), but a different number of neutrons, and therefore, different atomic weights. Although chemical properties are the same, radioactive and nuclear (radioactive decay) properties may be quite different for each isotope of an element.

Isotopic Enrichment - A process by which the relative abundance of the isotopes of a given element are altered, thus producing a form of the element that has been enriched in one particular isotope and depleted in its other isotopic forms.

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